I'm connected Wifi while flying home so lots of time to think.

Hi,  well what i can tell you from my experience with my 78, i did install a 5 speed keisler(tremec transmission with keisler's shifter, which now tremec has an offset shifter that should work if you go that route). The crossmember was a welded in one, so, first i tried the included instructions of putting in the tranny in much the same manner as the 4 speed(was "suppose" to be a direct bolt in with the directions of loosening the motor mounts and tilting the motor downward at the flywheel).. well, that didn't exactly work for me.. i ended up cutting the crossmember about 6 to 8 inches in from the frame, then taking the "center" piece and having 3 inch angle welded onto it, extended from the ends about 6 inches so i could drill two holes horizontally, and one vertically to bolt the "center" back to the welded crossmember pieces still on the car.  Made a world of difference, especially about 6 months later when a roll pin came out of the shifter and all i had was 3 and 4 gear(i contacted keisler about it after the 2nd time it happened, they sent me a replacement roll pin that has an e-clip, so i guess i was not the only one with that issue, and no doubt they've got it corrected), with the modified crossmember, i had the transmission out in about 40 minutes.. whereas if i had done it according to kiesler, i'd been looking at a little bit longer time(having to loosen or remove motor mounts, and possibly the fan so it wouldn't get into the radiator).... there are a few other members here that has converted to 5 speeds too... don't exactly remember how they went about it(but i think one of them already had a removable crossmember and not a welded one)...

The difference in shifting is night and day. The BW, Muncie and Richmond transmissions with the external linkage have to be guided through the nuetral gate. The Tremec only needs the shifter pulled straight back or pushed forward. If you try to shift like with your ST10 it will not work well. It only takes a few shifts to get the feel for it and you will absolutely love it. Actually you will have it mastered before the car comes off the jack stands. Tremec requires about 10 minutes of shifting through the gears under no load prior to driving. I ran mine easy doing a lot of shifting for 500 miles as per installation and break in instructions before hammering on it. With about 5000 miles on it now it is smooth and quiet,  do not miss my Muncie at all, especially when fueling up

I put one in the '81 a few years ago. My crossmember is a bolt in one. I think most '80-'82's were bolt in. The crossmember doesn't have the 2 holes in it for the exhaust pipes to pass thru.

It was the best investment I did for my car. The old T-10 4 speed was weak. I cracked mine in two during a hard launch.  Keisler is coming out with a RS 600 overdrive transmission soon. It isn't the Mexican Tremec. You may want to contact them and find out about the details with this transmission.

I installed a Keisler 5sp in 2004, best thing I did. As Darrell said, stay with Keisler because Tremec moved its plant to Mexico! Anyhow, after 2 times of pulling the trans with the cross member in. Like Jimmy, I cut the cross member and used 4 pieces of 3"/ 4"/1/4" flat steel and drilled 3/8" holes [4] and welded to the c/m. I did this because I installed the hydraulic throw out bearing, it makes a soft and easy peddle.  The exhaust is flanged at the headers and cut behind the c/m. I had end expanded to fit over other pipe and use S/S bands. Just for thouht, G-Force makes a C/M for C-3.

Surprised about the comments on the BW T-10 being a "weak link".    Isn't this the same tranny that many (non-GM) muscle cars used in the 60's and early 70's?  My 10 year plan involves a serious motor upgrade or rebuild (I'd say 300 - 350 HP) but that plan also included keeping and/or rebuilding the four speed  -- mostly just due to cost.  Maybe I'll need to rethink that plan?  Comments from anyone with a upgraded motor that's still running a stock T-10?  Other alternatives such as an upgrade rebuild or swapping in a Muncie?  

My transmission is not the original. It was in a 1982 Camaro. I had the transmission looked at and the rebuild guy says its only rated at 250 ft-pounds of torque.

I converted my 82 from a 200 HP Crossfire with maybe 200 ft LBS of torque, and a 700R4 26 spline, the first year GM used that tranny. I put in a GMPP 383/425HP with a Tremec TKO 600 behind it. To answer your question about torque, I almost went with the TKO 500, but in checking with Kessler,(which by the way i think they are Ace's. Especially Richard in Tech.) i discovered that the 500 was only rated up to 425 ft lbs. GMPP's 383/425 is rated at 460 ft lbs at 5K RPM. So, long story short i went with the 600 which is rated at 650 ft lbs. 

I have two of the Keisler products.  Both are great.  The first is the TKO 500 and it is in the 73 which has a bolt in cross member.  Altered the mount just a bit and all is good.  Great choice.  The second is their latest 5 speed and it is in the 74, which has a welded in cross member.  They recommended engine removal to install the new transmission and the advice was good.  That one works well also.  Both are great products and help with fuel consumption.  Highly recommend either 5 speed.  Keisler puts out good stuff; customer service is outstanding.

Curious.    I have an 82 that I'm installing a ZZ4, with a MassFlo Direct Injection system.  Headers and new Aluminum radiator.  I chose the ZZ4 and bought the the serp kit.  If I went with the ZZ383, I had concerns with the height of the intake.  did that cause any issue for you?